1. Field of the Invention
The invention relates to improved oiling systems for cylinder heads of certain HARLEY DAVIDSON motorcycle engines and methods for replacing oiling systems supplied for such engines by the manufacturer.
2. Description of the Prior Art
For many years, HARLEY DAVIDSON has manufactured twin cylinder air-cooled motorcycle engines wherein the front cylinder and rear cylinder are inclined at a 45.degree. angle relative to each other. The engines have overhead valves. The overhead valves for the particular engines referred to have been oiled by means of a first oil tube connected to a single oil outlet located in the crankcase housing at the base of the rear cylinder and extending to an oil inlet of the head of the rear cylinder. Oil is forced through internal paths in the head of the rear cylinder. Some of the oil forced into the head of the rear cylinder returns to the crankcase, through the push rod tubes and internal return paths of that cylinder and the rest of it passes through an oil outlet of the rear cylinder head through a second tube into an oil inlet of the front cylinder head. Ordinarily, this oiling arrangement has been adequate. However, it is well known to motorcycle mechanics that the rear cylinder of such HARLEY DAVIDSON engines runs hotter than the front cylinder, (if both cylinders are adequately lubricated) because the front cylinder blocks air that would otherwise circulate through the fins of the cylinder and more effectively cool it. Consequently, the oil in the rear cylinder head is substantially heated before it reaches the front cylinder head. Under extremely high temperature engine operating conditions, the above oiling system causes the oil reaching the head of the front cylinder to be too hot to ensure adequate lubrication thereof.
Accordingly, it is an object of the invention to provide an improved oiling system which avoids undue heating of oil fed to the front cylinder head of a HARLEY DAVIDSON V-type engine having only one oil outlet in the crankcase housing.
It is quite common for HARLEY DAVIDSON motorcycle enthusiasts to customize their motorcycles often, considerably altering the original design of the motorcycles to provide radically modified appearance and to display the customized motorcycles at various shows and the like. The customized motorcycles frequently are altered also to greatly improve the mechanical operation thereof, and the ultimate objective of modification of such motorcycles as described above is to provide uniquely attractive machines having excellent mechanical performance and reliability.
It is another object of the invention to provide an attractive improved oil circulation system for cylinder heads of certain HARLEY DAVIDSON twin cylinder motor engines having overhead valves and only a single oil outlet from the crankcase thereof.
The basic design of the V-type 45.degree. HARLEY DAVIDSON engine is very old, having been used on HARLEY DAVIDSON motorcycles since the early part of this century. Although many other manufacturers of popular motorcycles have designed vastly improved, more modern motorcycle engines, HARLEY DAVIDSON motorcycles have retained a mystique among many motorcycle enthusiasts which has been unmatched by any other brands of motorcycles. Despite various disadvantages of the above-described V-type 45.degree. HARLEY DAVIDSON Model 74 motorcycles having the above-described engine remain highly popular, despite the fact that the engine does not incorporate certain aspects of modern motorcycle technology, including provisions by HARLEY DAVIDSON of dual oil outlet ports in the crankcase of other motorcycle engines for separate oil tubes connected to the front and rear cylinder heads. In fact, many, if not most improvements and innovations in the narrow art of HARLEY DAVIDSON V-type engines arise from the ranks of owners of such machines and mechanics who work on them, rather than from the manufacturer of HARLEY DAVIDSON motorcycles.